Preparation and application of sodium sulfonate functionalized covalent organic framework material

Abstract

The invention provides preparation and application of a sodium sulfonate functionalized covalent organic framework material. On the basis of a Schiff base condensation reaction between amido and aldehyde group, a hydroxyl covalent organic framework material is successfully synthesized under an acid catalysis condition, and the material is subjected to in-situ functional modification through an in-situ nucleophilic substitution reaction, so that the sodium sulfonate functional covalent organic framework material is prepared. The material has a good adsorption effect on cationic dyes, and the adsorption removal rate can reach 99% or above.

Description

Technical Field

[0001] The present invention relates to the preparation of a sulfonate-functionalized covalent organic framework material and its application as an adsorbent for adsorbing cationic dyes, belonging to the technical field of functional organic porous materials. Background Art

[0002] With the rapid development of industry, organic pollutants such as dyes have become the most common industrial pollutants in water bodies. Industries such as textile dyeing, papermaking, printing, and food processing are recognized as the main sources of organic dye pollutants. Common organic dyes include anionic dyes such as Congo Red (CR), Methyl Orange (OM), and Fluorescein Sodium Salt (FS); and typical cationic dyes such as Crystal Violet (CV), Methylene Blue (MB), Rhodamine B (RhB), and Malachite Green (MG). Due to their excellent water solubility, low biodegradability, and high toxicity, these dyes are difficult to effectively remove from water bodies. Even a small amount of organic dyes discharged into environmental water bodies will cause serious water pollution problems and ultimately pose carcinogenic and mutagenic risks to human health. In view of this, developing efficient separation technologies and new adsorbents to remove organic dye pollutants from wastewater remains a crucial task.

[0003] Covalent Organic Frameworks (COFs) materials are porous organic solid materials with a specific lattice structure and high specific surface area assembled from customizable building blocks through covalent bonds. COFs have attracted extensive research attention in the fields of gas adsorption, catalysis, and separation due to their excellent chemical stability, adjustable pore size, high porosity, low density, and large specific surface area. Given their regular and customizable pore structures, COFs are expected to become a powerful platform for designing new adsorbent materials with performance superior to traditional adsorbents. By introducing specific functionalized building blocks (such as charged groups) to construct ionic covalent organic frameworks, the ability to capture ions through electrostatic interactions can be imparted to them. Such COFs not only have a clear pore structure but also have ion groups distributed along the channels, providing abundant binding sites for the adsorption of target ions, thereby achieving effective capture of target ions. Based on this, in this study, a hydroxyl-functionalized covalent organic framework material was successfully synthesized based on the Schiff base condensation reaction between amino groups and aldehyde groups under acidic catalytic conditions, and it was functionalized by an in-situ nucleophilic substitution reaction to prepare a sulfonate-functionalized covalent organic framework material. By introducing sulfonic acid groups into the covalent organic framework, it is endowed with abundant anion binding sites to achieve selective adsorption and removal of cationic dyes in the water environment. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of a sulfonate-functionalized covalent organic framework material to improve the functionality of the COF.

[0005] Another object of the present invention is to provide the application of the sulfonate-functionalized covalent organic framework material as an adsorbent for adsorbing and removing cationic dyes.

[0006] I. Preparation of sulfonate-functionalized covalent organic framework material 1) First, 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde and 4-bromo-1-butanesulfonic acid are co-dissolved in an organic solvent, and then sodium carbonate is added; three freeze-pump-thaw cycles are carried out for degassing, and the system is sealed; the system is transferred to an oven, heated to 40 °C, and after reacting at a constant temperature for 72 - 120 h, it is cooled to room temperature in 2 h to end the reaction; The molar ratio of 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde and 4-bromo-1-butanesulfonic acid is 1:(1 - 1.5):(7 - 7.5); The organic solvent is a mixture of mesitylene and acetonitrile, and the volume ratio of mesitylene to acetonitrile is 1:(2.5 - 3); The molar ratio of sodium carbonate to 1,3,5-tris(4-aminophenyl)benzene is 1:(15 - 20); 2) The system after the reaction in step 1) is taken out of the oven, filtered, washed with absolute ethanol, and the product is vacuum dried at 50 - 60 °C to obtain a crude product; 3) The crude product obtained in step 2) is subjected to Soxhlet extraction, and then vacuum dried at 60 - 70 °C for 10 - 15 h to obtain the sulfonate-functionalized covalent organic framework material, denoted as COF-SO3Na.

[0007] Synthesis mechanism: The sulfonate-functionalized covalent organic framework material is prepared from 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde and 4-bromo-1-butanesulfonic acid in a mesitylene and acetonitrile solvent through two steps: a Schiff base condensation reaction catalyzed by 4-bromo-1-butanesulfonic acid and an in-situ nucleophilic substitution reaction involving 4-bromo-1-butanesulfonic acid.

[0008] The reaction steps are as follows: (1) Schiff base condensation (2) In-situ nucleophilic substitution .

[0009] II. Structural characterization of sulfonate-functionalized covalent organic framework material The X-ray diffraction pattern is as Figure 1As shown, it can be seen that COF-SO3Na shows diffraction peaks at 2.82 o , 4.89 o , 5.69 o , 7.49 o , corresponding to the 100, 110, 200, and 120 crystal planes respectively. The broad peak around 26 o belongs to the 001 crystal plane. The above results indicate the successful preparation of COF-SO3Na and its high crystallinity after modification, further demonstrating the successful synthesis of COF-SO3Na.

[0010] The Fourier transform infrared spectrum is as shown in Figure 2 . It can be seen that the absorption peak at 3433.54 cm -1 is attributed to the stretching vibration peak of -OH. Compared with COF-OH, the peak intensity of COF-SO3Na at this position is significantly weakened, indicating that -OH has reacted and -SO3Na has been successfully modified into COF; the diffraction peak of COF-SO3Na at 1613.78 cm -1 is attributed to the stretching vibration peak of -C=N, which is formed by the Schiff base reaction; the peaks at 2921.69 cm -1 and 2871.76 cm -1 appear and are attributed to the -CH stretching vibration of the alkyl group. The new peaks at 1013.67 cm -1 and 539.00 cm -1 are caused by the stretching vibration of O=S=O, which also confirms that -SO3Na has been successfully modified into COF, indicating the successful preparation of COF-SO3Na.

[0011] The thermogravimetric analysis diagram is as shown in Figure 3 . It can be seen that COF-SO3Na still maintains structural stability at around 370°C, indicating that COF-SO3Na has good thermal stability.

[0012] The scanning electron microscopy image is as shown in Figure 4 . It can be seen that the material presents a spherical morphology structure with a diameter range of 1.5 - 2 nm.

[0013] III. Adsorption Performance Evaluation of Sulfonate-Functionalized Covalent Organic Framework Materials 1. Adsorption of Cationic Dyes 1) Preparation of cationic dye solutions: Crystal violet (CV), malachite green (MG), and methylene blue (MB) are respectively dissolved in distilled water to prepare cationic dye stock solutions with a concentration of 100 mg / L. Appropriate amounts of distilled water are used for dilution to prepare MG working solutions with a concentration of 50 mg / L, CV working solutions with a concentration of 30 mg / L, and MB working solutions with a concentration of 20 mg / L; 2) Cationic dye adsorption process: Take 20 mL of the working solutions of MG, CV or MB, adjust their pH to about 8.0, and mix them evenly with 10 mg of the adsorbent (COF-SO3Na) respectively. Oscillate on a constant temperature oscillator for 30 min to reach adsorption saturation. Then centrifuge to separate the adsorbent, take the supernatant, and detect the absorbance of the residual dye in the supernatant by UV-vis.

[0014] The UV spectra of the material before and after adsorption of the three cationic dyes are as Figure 5 shown. Under the above adsorption conditions, before adsorption, the absorbances of the 50 mg / L MG, 30 mg / L CV and 20 mg / L MB working solutions are 0.6156, 2.5016 and 2.9556 respectively. After adsorption, the absorbances of the solutions become 0.0554, 0.069 and 0.9441. It can be seen that the absorbance values differ greatly before and after adsorption, and almost all are adsorbed, indicating that the material has high adsorption and removal ability for cationic dyes. From Figure 5 the inset, it can be seen that the colors of the solutions almost become colorless after adsorption of MG and CV dyes, further indicating that almost all the dyes are adsorbed.

[0015] The adsorption mechanism is as follows: Under alkaline conditions (pH = 8), the sodium sulfonate-functionalized covalent organic framework material is negatively charged and binds to the cationic dye through electrostatic interaction.

[0016] 2. Adsorption selectivity 1) Preparation of mixed solutions of anionic and cationic dyes: Dissolve 3 mg of methyl orange (MO) and 3 mg of CV and MB in distilled water respectively to prepare MO-CV and MO-MB mixed solutions with a concentration of 30 mg / L.

[0017] 2) Adsorption process: Take 20 mL of the above mixed solutions (adjust the pH to about 8.0), mix them evenly with 10 mg of COF-SO3Na material respectively, and oscillate on an oscillator for 30 min to reach adsorption saturation. Then centrifuge to separate the adsorbent, take the supernatant, and detect the absorbance of the supernatant by UV-vis.

[0018] The UV spectra of the two mixed dyes before and after adsorption are as Figure 6。Under the above adsorption conditions, when MO coexists with CV and MB respectively, before adsorption, the colors of the MO-CV mixed solution and the MO-MB mixed solution are brown and dark green respectively, and the colors of the solutions after adsorption are orange and yellowish green. It can be seen from the ultraviolet absorbance spectra that the absorption peak intensities of CV and MB decrease significantly after adsorption, while the absorption peak intensity of MO hardly changes, indicating that the material almost completely adsorbs the cationic dyes CV and MB, while hardly adsorbing MO.

[0019] The above experiments show that the material has good selectivity and can achieve efficient adsorption of cationic dyes under complex conditions, indicating that the material has broad application prospects for adsorbing cationic dyes in complex environments.

[0020] The present invention has the following beneficial effects compared with the prior art: 1. The present invention for the first time synthesizes a sodium sulfonate-functionalized covalent organic framework material by a one-pot solvothermal method without post-modification reaction; 2. The present invention selects sodium carbonate as an inducer to ensure the successful synthesis of the sodium sulfonate-functionalized covalent organic framework material, which has high crystallinity and stability at the same time; the selected 4-bromo-1-butanesulfonic acid can be used both as a functionalization modification raw material and as a reaction catalyst; 3. The sodium sulfonate-functionalized covalent organic framework material synthesized by the present invention can preferentially remove cationic dyes under the coexistence conditions of anionic and cationic dyes, and the removal rate can reach more than 99%. Brief Description of the Drawings

[0021] Figure 1 is the X-ray diffraction pattern of the sodium sulfonate-functionalized covalent organic framework material in the embodiment of the present invention.

[0022] Figure 2 is the Fourier transform infrared spectrum of the sodium sulfonate-functionalized covalent organic framework material in the embodiment of the present invention.

[0023] Figure 3 is the thermogravimetric analysis diagram of the sodium sulfonate-functionalized covalent organic framework material in the embodiment of the present invention.

[0024] Figure 4 is the scanning electron microscope image of the sodium sulfonate-functionalized covalent organic framework material in the embodiment of the present invention.

[0025] Figure 5 is the ultraviolet spectrum of the sodium sulfonate-functionalized covalent organic framework material in the embodiment of the present invention before and after adsorbing three cationic dyes.

[0026] Figure 6 is the ultraviolet spectrum of the sodium sulfonate-functionalized covalent organic framework material in the embodiment of the present invention before and after adsorbing two cationic dyes in the presence of methyl orange. Detailed Embodiments

[0027] The present invention will be further explained below in conjunction with specific embodiments. Embodiment

[0028] 1) 21.09 mg (0.06 mmol) of 1,3,5-tris(4-aminophenyl)benzene, 13.95 mg (0.08 mmol) of 2,5-dihydroxyterephthalaldehyde, and 96.2 mg (0.44 mmol) of 4-bromo-1-butanesulfonic acid were successively added to a 50 mL reaction tube, mixed evenly. Subsequently, 8 mL of mesitylene and 20 mL of acetonitrile were successively added to the above reaction tube, and ultrasonic treatment was carried out to completely dissolve the solid. Then, 1 mL of a sodium carbonate solution with a concentration of 357 mg / L was added. 2) Three freeze-pump-thaw cycles of degassing were carried out separately to seal the system. The system was transferred to an oven, heated to 40 °C, and reacted at a constant temperature for 72 h. Then, the temperature was decreased to room temperature over 2 h to end the reaction. 3) The reaction system was taken out of the oven, subjected to vacuum filtration, washed 4 times with absolute ethanol, and the product was dried under vacuum at 60 °C for 12 h to obtain a crude product. 4) The obtained crude product was further subjected to Soxhlet extraction with dichloromethane for 48 h, and then dried under vacuum at 60 °C for 12 h. Finally, COF-SO3Na was obtained.

[0029] The structural characterization and performance evaluation are shown above.

Claims

1. A preparation method of a sodium sulfonate-functionalized covalent organic framework material, characterized in that, It includes the following steps: 1) First, dissolve 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde and 4-bromo-1-butanesulfonic acid in an organic solvent, and then add sodium carbonate; perform three freeze-pumping-thaw cycles for degassing, and seal the system; transfer the system to an oven, heat it to 40 °C, keep it at a constant temperature for reaction for 72 - 120 h, then cool it for 2 h to room temperature to end the reaction; 2) Take out the system after the reaction in step 1) from the oven, filter it, wash it with absolute ethanol, and vacuum-dry the product at 50 - 60 °C to obtain a crude product; 3) Perform Soxhlet extraction on the crude product obtained in step 2), and then vacuum-dry it at 60 - 70 °C for 10 - 15 h to obtain a sodium sulfonate-functionalized covalent organic framework material, denoted as COF-SO3Na.

2. The preparation method of a sodium sulfonate-functionalized covalent organic framework material according to claim 1, characterized in that, The molar ratio of 1,3,5-tris(4-aminophenyl)benzene, 2,5-dihydroxyterephthalaldehyde and 4-bromo-1-butanesulfonic acid is 1:(1 - 1.5):(7 - 7.5).

3. The preparation method of a sodium sulfonate-functionalized covalent organic framework material as described in claim 1, wherein, The organic solvent is a mixture of mesitylene and acetonitrile, and the volume ratio of mesitylene to acetonitrile is 1:(2.5 - 3).

4. The preparation method of a sulfonate-functionalized covalent organic framework material according to claim 1, characterized in that, The molar ratio of sodium carbonate to 1,3,5-tris(4-aminophenyl)benzene is 1:(15 - 20).

5. A sodium sulfonate-functionalized covalent organic framework material prepared by the method according to claim 1, characterized in that, The structural formula of the material is as follows: 。 6. Application of a sodium sulfonate-functionalized covalent organic framework material prepared by the method according to claim 1 in adsorbing cationic dyes.

Images